JP H03-293542 A discloses a technique of inspecting defects of the surface of a camshaft. In the technique of JP H03-293542 A, the cam surface is divided into multiple inspection sections considering the use of the cam, and special optical instruments are used for each of the inspection sections. Therefore, the best inspection condition for the camshaft as an object to be inspected can be chosen by changing the criterion for determining the defects in accordance with the inspection sections. Thus, the technique provides the defect inspection considering working condition or unique characteristics of the object.
JP 2008-233106 A discloses a technique of inspecting defects of the surface of a work including curved surface at the periphery thereof. In the technique of JP 2008-233106 A, conditions for an image processing are changeable in response to light and shade in the curved surface which is inclined against the imaging device, so that the defects on the curved surface can be detected.
Unfortunately, the conventional techniques do not adequately take into account the image distortion occurred in the image of the curved portion, and thus the shape, especially dimension, of the defect in the curved portion may be misdetected. Moreover, the image distortion may be occurred according to the positional relationship, such as distance or angle, between the camera for picking up the image and the work, so that it is difficult to accurately detect the defects.